The main objective of this project is to increase our understanding of mechanism involved in the metabolism of porphyrins in normal and disease states. Previous studies have shown that in porphyria cutanea tarda (PCT), a disease characterized by excess hepatic porphyrin synthesis, hepatic delta-aminolevulinic acid (ALA) synthetase activity is not elevated. We propose to determine the presence and significance of a pathway in mammals for the synthesis of ALA that differs from the usual condensation of glycine and succinyl-CoA. We plan to study the direct synthesis of ALA from such 5-carbon compounds as alpha-ketoglutarate and gamma,delta-dioxovalerate in mitochondria isolated from normal and porphyrin livers. The enzymatic decarboxylation of uroporphyrinogen is defective in patients with PCT and evidence suggests that more than one enzyme may be required for this 4 step reaction. With purified preparations of uroporphyrinogen decarboxylase (URODECARB) we will do kinetic studies using partially decarboxylated porphyrinogens as substrates to evaluate the hypothesis that at least two URODECARB enzymes exist. In association with these studies we plan to look for a multi-enzyme complex consisting of uroporphyrinogen I synthetase, uroporphyrinogen III cosynthetase and URODECARB which might have a regulatory function in heme biosynthesis. Finally we intend to study the incorporation of carbon-13 labeled precursors into porphyrins in vivo in patients with PCT and their relatives.